As a high-power semiconductor device, for example, a semiconductor device in which a semiconductor chip which forms a power supply transistor such as a power MOSFET (Metal Oxide Semiconductor Field-Effect-Transistor), an IGBT (Insulated Gate Bipolar Transistor), or a bipolar power transistor is incorporated in a sealing body is known.
A power MOSFET device has a structure in which a power MOSFET chip is incorporated in a sealing body. As a power MOSFET device, a structure in which a metal member serving as a drain terminal is exposed on the bottom surface of a sealing body made of insulating resin, and a source lead terminal and a gate lead terminal are disposed on one side of the sealing body is known. In the structure, the source lead terminal and the gate lead terminal are bent at a part, and the part is exposed on the upper surface of the sealing body. The source lead terminal and the gate lead terminal extending in the sealing body are respectively electrically connected to a source electrode and a gate electrode on the upper surface of a semiconductor chip which is fixed on the metal member. These lead terminals are bonded onto the source electrode and the gate electrode by ultrasonic compression bonding via gold (Au) bumps uniformly disposed by a ball bonding method using bonding wires (hereinafter, simply referred to as wires). More specifically, after distal ends of the wires are connected onto the source electrode and the gate electrode by a thermocompression bonding method, the wires are pulled to be ruptured so that stud-type bump electrodes are formed, and the bump electrodes are connected to the lead terminals by the ultrasonic method. For example, this is disclosed in Japanese Patent Application Laid-Open Publication No. 2000-223634 (Patent Document 1). Other methods for connecting electrodes of a semiconductor chip with lead terminals include a method in which the electrodes of the semiconductor chip are electrically connected to the lead terminals by solder. In this method, since metal compounds are formed in the boundary surfaces between the electrodes and the solder and the connection property is degraded, in order to prevent generation of the metal compounds, an under barrier metal layer (Under Bump Metal: UBM layer) formed by sequentially stacking layers of, for example, titanium (Ti) and nickel (Ni) in this order from below is provided on the electrodes. However, the manufacturing cost of the semiconductor device increases since the UBM layer is formed by a process such as sputtering.